fix(helpers): should be able to highlight first row (0)

[ghiscoding]

• calling highlightRow(0) was not highlighting the row when it should
• fixes Aurelia-Slickgrid issue #527

[codecov]

Codecov Report

Merging #268 (36409db) into master (20564a3) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #268   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          209       209           
  Lines        12119     12119           
  Branches      4170      4170           
=========================================
  Hits         12119     12119           

Impacted Files	Coverage Δ
packages/common/src/services/grid.service.ts	100.00% <100.00%> (ø)

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